Re: [PATCH 2/2] kthread: Drop warning on cpumask allocation failure in kthread_affine_node()

[Bradley Morgan <brads@mainlining.org>]

On 14 September 2026 13:09:41 BST, Quchaosheng <quchaosheng000406@163.com>
wrote:
>kthread_affine_node() warns when zalloc_cpumask_var() fails:
>
>  if (!zalloc_cpumask_var(&affinity, GFP_KERNEL)) {
>          WARN_ON_ONCE(1);
>          return;
>  }
>
>The allocation uses GFP_KERNEL, so it can fail under memory pressure or
>fault injection.  A failed allocation is a recoverable condition and not a
>kernel bug, so the warning is noise.  syzbot reports it for a WireGuard
>NAPI thread:
>
>  WARNING: kernel/kthread.c:359 at kthread_affine_node+0x200/0x2e8
>  CPU: 0 PID: 5207 Comm: napi/wg2-0
>  Call Trace:
>   alloc_cpumask_var_node+0xfc/0x138
>   zalloc_cpumask_var
>   kthread_affine_node+0x148/0x2e8
>   kthread+0x29c/0x3d4
>   ret_from_fork+0x10/0x20

Interesting.

>
>The other two callers of zalloc_cpumask_var() in this file, in the kthread
>preferred affinity and kthreads_online_cpu() paths, return -ENOMEM without
>a warning.  kthread_affine_node() returns void, so it cannot report the
>error either, and it only skips the affinity setup for this thread. 
>Return
>early without warning, matching those callers.

Makes sense.

>
>Reported-by: syzbot+37ca7ae3e98cb65c3209@syzkaller.appspotmail.com
>Closes: https://syzkaller.appspot.com/bug?extid=37ca7ae3e98cb65c3209
>Signed-off-by: Quchaosheng <quchaosheng000406@163.com>



>---
> kernel/kthread.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
>diff --git a/kernel/kthread.c b/kernel/kthread.c
>index a3f95c904..f735a74b6 100644
>--- a/kernel/kthread.c
>+++ b/kernel/kthread.c
>@@ -355,10 +355,8 @@ static void kthread_affine_node(void)
> 	if (WARN_ON_ONCE(kthread_is_per_cpu(current)))
> 		return;
> 
>-	if (!zalloc_cpumask_var(&affinity, GFP_KERNEL)) {
>-		WARN_ON_ONCE(1);
>+	if (!zalloc_cpumask_var(&affinity, GFP_KERNEL))
> 		return;
>-	}

Uhh, I'm unsure about this. 

The warn may be intended?

Perhaps you could warn -> info? 

Because people may prefer to know if it's broken.

I'm not comfortable adding a tag until the maintainers have a input



> 
> 	mutex_lock(&kthread_affinity_lock);
> 	WARN_ON_ONCE(!list_empty(&kthread->affinity_node));
>
>
>

--- Thanks!
https://lore.kernel.org/all/EE579805-42F2-4C58-B752-F28779EEB717@grrlz.net/